Injection devices are known in the prior art that inject treatment substances, such as vaccines, antibiotics or vitamins, directly into eggs, in order to limit the mortality rate or increase embryo growth. Such devices conventionally comprise an injection head which comprises a plurality of vertically moveable injectors above a routing conveyor of eggs to be treated, the eggs being conventionally positioned in cells of so-called incubation trays. Patent document FR 2 873 894 particularly proposes an injection head wherein each injector is equipped with its own movement system to move the injector from a raised position to an injection position wherein its needle can inject a substance into the egg. The needle is housed in a telescopic guiding and protection bush or tube. This tube is mounted in a moveable manner with respect to the needle between a retracted position wherein the needle is projecting with respect to the distal end of the tube, and an idle position wherein the tube surrounds at least the distal part of the needle. The tube is subject to elastic stress by elastic means towards its idle position. When the injector has lowered to its injection position, the tube presses via its distal end against the egg and moves to its retracted position.
In the poultry industry, particularly the chicken industry, the incubation trays contain a non-negligible proportion of “clear” eggs, i.e. unfertilised eggs, and/or “non-live” eggs, i.e. comprising dead embryos. So as to only treat the fertilised and live eggs on the trays, and thus optimise the treatment substance consumption, the abovementioned patent document proposes to successively perform, for each tray, a candling operation of the eggs on a tray, in order to differentiate fertilised and live eggs from clear or non-live eggs, a clear or non-live egg removal operation from the trays, a detection operation of the remaining eggs on the tray and, finally, an injection operation of the remaining eggs detected. The detection of the remaining eggs is carried out upstream from the injection device by means of a transversal ramp of optical detectors capable of differentiating empty cells from cells containing an egg. The injectors are then selectively controlled by a control unit according to the signals generated by the detectors, and received, processed and stored by the control unit. For each cell containing an egg, the control unit starts an injector injection cycle, said cycle comprising the lowering of the injector to its injection position, the injection of the substance via the needle, and the return to the raised position.